The present invention relates to a sensor equipped axle unit having a built-in motor of in-wheel type including a hub bearing assembly, a reduction gear unit and an electric motor combined together in a unitary structure and, more particularly, to the control technology in controlling the traveling stability of an electrically driven automotive vehicle.
As means to reduce the environmental loading, the automotive vehicle is expected to transform from a power type utilizing a combustion engine to a different power type utilizing an electric motor in the future. Under these circumstances, the axle unit having an in-wheel type motor built therein has been suggested as a wheel support bearing assembly for the support of a vehicle drive wheel of an electrically powered automotive vehicle. (See, for example, the Patent Documents 1 and 2 quoted below.) When this suggested axle unit having the in-wheel type motor built therein is employed in the vehicle drive wheels of an electrically powered automotive vehicle, the vehicle drive wheels can be driven individually and independently of each other and, therefore, the use of a rather bulky drive transmitting mechanism such as, for example, a propeller shaft and/or a differential gear unit can be dispensed with from the automotive vehicle, allowing the latter to be manufactured lightweight and compact in size.
In association with the standard wheel support bearing assembly utilized in combustion engine vehicles, various controls such as, for example, suspension control and ABS (anti-lock brake system) are employed as a control technology for controlling the stability of each automotive vehicle. Detection of various operating statuses of the automotive vehicle with numerous sensors secured to the vehicle body structure is also performed so that the engine, brakes and/or steering wheel can be controlled based on a result of such detection.    [Patent Document 1]
JP Laid-open Patent Publication No. 2005-7914    [Patent Document 2]
JP Laid-open Patent Publication No. H05-332401 (FIGS. 1-3)
The electromotor driven type has a response characteristic higher than that of the combustion engine driven type and, therefore, the suspension control and/or the ABS control, when introduced into the electromotor driven vehicle, is/are effective to allow the attitude of the automotive vehicle to assume a higher stability than that accomplished when introduced into the combustion engine driven vehicle. In order to increase the precision of the suspension control and the ABS control, it is necessary to accurately measure the force acting on the automotive vehicle and then to perform the control based on a result of such force measurement.
The force acting on the automotive vehicle referred to above is in large part developed between a wheel tire and a road surface. This force is available in the form of a force acting in a direction of travel of the automotive vehicle, a cornering force acting in a direction perpendicular to the direction of travel of the automotive vehicle (a force acting in a direction axially of a vehicle drive wheel), and a normal force acting in a direction perpendicular to a ground plane a vertical force). In addition, it may be available in the form of an air drag dependent on the travelling velocity and an aerodynamic force brought about by a wind blowing in nature, but those are low in steady state. Accordingly, for the control to stabilize the vehicle attitude, detection of the forces acting between the wheel tire and the road surface in three axis directions referred to above with high response is sufficient.
However, measurement of the forces acting in the automotive vehicle with sensors fitted to the vehicle body structure such as hitherto practiced is nothing other than measurement of vibrations transmitted to the vehicle body structure through the suspension system and the chassis and, therefore, a time lag tends to occur in the resultant measurement. Because of this, a problem has been encountered with in that the response to control tends to be delayed if the resultant measurement involving the time lag is utilized in the stability control.